(1) Field of the Invention
The present invention relates to a heat shield which provides thermal insulation from a heat source. In particular, the present invention relates to improvements in the structure and method of manufacturing a heat shield. The improvements include manufacturing the heat shield from a plurality of layers of substantially identical metallic or other formable sheets with each sheet having stand-offs formed on each side to thereby provide air pockets between adjacent sheets of the shield that enhance the thermal resistance and reduce the shield weight. Non-planar heat shields, or shields formed with angular or curved configurations, are produced by preforming the sheets prior to their assembly into the layered sheet shield to prevent the collapse of the air pockets between adjacent sheets which would otherwise occur if the sheets were first layered and then formed into their curved or angular non-planar configuration. Further, the production of the non-planar heat shields may include a final forming step which biases the sheets toward one another to increase the inter-laminar friction and thereby dampen vibration and strengthen the heat shield structure.
(2) Description of the Related Art
Heat shields are often employed to separate objects that are sensitive to heat from sources of heat close to those objects. Various heat shields have been developed for thermal insulation purposes. For instance, U.S. Pat. No. 2,179,057 discloses a thermally insulating laminate comprised of sheets of asbestos material having stand-offs extending from one side of each sheet. The stand-offs space the asbestos sheets in the laminate to create air pockets between the sheets and thereby increase the thermal resistance and decrease the weight to size ratio of the laminate. The laminate is assembled such that the stand-offs of each adjacent sheet are oriented in mutually opposed directions to maximize the air pocket volumes.
The aforementioned asbestos laminate has several disadvantages foremost of which is that recent focus on the health effects of exposure to asbestos has reduced the desirability of asbestos. Further, since the stand-offs are only formed on one side of the sheets, extra care must be taken during assembly to achieve the required orientation to form the air pockets between the lamina.
U.S. Pat. No. 2,926,761 discloses another thermally insulating laminate. This laminate is comprised of a honeycomb core made from 0.002 inch thick stainless steel foil. Both ends of the honeycomb cells are capped by additional stainless steel foil lamina which form the exterior sides of the heat shield. This configuration is disadvantaged in that it is relatively expensive to manufacture the honeycomb core. In addition, because the laminate is not divided into multiple sections through its thickness, significant heat transfer may take place through the heat shield via the honeycomb cell walls thereby reducing the overall thermal resistance of the heat shield.
U.S. Pat. No. 4,703,159 discloses yet another thermally insulating laminate primarily intended for use in space vehicles. The laminate is comprised of dimpled 0.002 inch thick nickel-based alloy foil stacked between thicker nickel-based alloy side sheets which provide increased crush resistance to the heat shield as well as a neat appearance. The lamina are brazed together in this laminate to increase the overall stiffness of the structure. However, brazing the lamina reduces the thermal resistance of the heat shield and increases manufacturing costs.
U.S. Pat. No. 5,011,743 discloses still another heat shield configuration comprised of dimpled 0.002 inch thick aluminum foil. One alternate embodiment employs a scrim attached to one side of the heat shield. Another alternate embodiment uses a 0.020 inch thick carrier plate on one side to increase the heat shield crush resistance. With each of these alternate embodiments, a separate material must be stocked and handled which increases manufacturing costs. The addition of the scrim or carrier plate also adds weight to the heat shield. In addition, with the carrier plate embodiment, the thermal resistance through the heat shield is reduced because the heat travels around the edges of the foil via the carrier plate.
As alluded to above, each of these prior art heat shields has disadvantages. Either the heat shield is unnecessarily expensive, unnecessarily heavy, or has an unnecessarily reduced thermal resistance.
Each of the aforementioned patent disclosures provides a sufficient method of manufacture to produce planar heat shields. However, non-planar heat shields are frequently desired to conform to the shape of a particular component which must be insulated. If a typical prior art planar heat shield is bent to conform to the shape of the component, the air pockets between the lamina collapse and the lamina come into contact with each other at the bend, thereby reducing the thermal resistance. Since the air pockets provide the majority of the thermal insulation, collapse of the air pockets significantly reduces the overall thermal resistance of the heat shield. Therefore, an improved non-planar heat shield which eliminates or reduces the potential for air pocket collapse is desirable.